Accompanying the development of advanced medical techniques, candidiasis has emerged as a significant nosocomial infection that causes considerable morbidity and mortality among immunocompromised patients. Candida blood stream infections are increasing in frequency and are associated with high mortality. Oral candidiasis is an extremely common opportunistic infection in AIDS patients. Despite the prevalence of these infections, treatment options are limited. With the exception of the newly developed echinocandins, the antifungal drugs currently in use are limited by toxicity and natural or acquired resistance. Therefore, development of new antifungal drugs is of great importance. Our long-term goal is to develop new drug therapies for fungal infections. The difficulty in achieving this goal is that fungi use mechanisms for gene expression and cell growth that are similar if not almost identical to those used by mammalian cells. An essential process shared by all eukaryotes is the modification of the 3'ends of mRNAs by cleavage of longer precursor molecules and the subsequent addition of a tract of adenosine residues. Acquisition of this poly(A) tail is important for accumulation of mature mRNA, its export from the nucleus, its utilization in translation of protein, and its removal when the mRNA is no longer needed by the cell. In the last few years, our research and that of others has identified most, if not all, of the subunits of this processing complex and revealed a remarkable conservation between the yeast Saccharomyces cerevisiae and metazoans. However, we have also found significant species-specific differences, suggesting that inhibitors uniquely interfering with fungal mRNA 3'end formation could be found. In this study, we will develop a high throughput assay to screen S. cerevisiae for small-molecule inhibitors of mRNA polyadenylation. This assay will be based on an existing reporter construct used in our laboratory to detect defects in mRNA 3'end processing. Once the screen is optimized for a 384-well format, we will use it to screen a collection of 140,000 chemicals available through the Broad Institute of Harvard and M.I.T. We will use several in vivo and in vitro assays as secondary screens to confirm that hit molecules are indeed targeting mRNA 3'end formation. We will then determine if the candidate molecules inhibit growth and mRNA 3'end formation in the pathogen C. albicans, and construct a reporter for polyadenylation inhibitors that can be employed in additional large-scale screens directly in Candida. We expect that this study will yield a novel class of anti-fungal drugs and thus address the pressing need for additional inhibitors of pathogenic fungi. Candida has recently emerged as a significant opportunistic pathogen that causes considerable morbidity and mortality in immunocompromised patients. Unfortunately, treatment options for fungal diseases are extremely limited and, compounding this problem, resistance to some of the best anti-fungal drugs is emerging. By taking advantage of certain differences in how fungi and human cells synthesize messenger RNA, we propose to conduct a high throughput screen for a novel class of anti-fungal drugs and thus address the pressing need for additional inhibitors of pathogenic fungi.